Two areas are currently being investigated: a) Size of infectious particle: Cells of Cryptococcus neoformans were seeded into 250 gm of sterile soil. Following 0-30 wks incubation at room temperature the seeded soil is aerosolized inside a Tri-R Infectious Apparatus chamber. Dust clouds are sampled for 15-30 seconds with an Anderson Air Sampler from which the sizes and distribution of viable airbone yeast particles is determined. To date an appreciable number of cells 0.6 to 3.0 um in diameter have been isolated. We believe that particles of this size are capable of deep lung deposition. 2) GI tract as a portal of entry: Mice were inoculated intragastrically with C. neoformans. At weekly intervals up to one year post-inoculation feces were assayed for C. neoformans. Throughout this time period 5-10% of the animals continuously shed viable cells of C. neoformans. It appears that in these animals the cecum is the reservoir. Viable yeast cells shed fecal pellets for 6-8 months after being excreted from the animal.